That's fair enough but it's an arbitrary place to draw the line. If you pay tax in the US then you build weapons. If you live in a country that doesn't either build weapons or pay someone else to build them for you, then you'll soon be getting told what do by some country that does, and building weapons is one of the things they'll probably tell you to do.
It's totally possible. There's an defense contractor in my area where all the work at the local office is on non-defense government projects.